first makes sure that yor fuel pump can handle the demand of filling two carbs. next if the car really hooks up you may need to change the needle and seat to high flow becuase the primarys will uncover with a lot of acceleration,
the kits for tuning the carbs are around $50.00 each (you will need two kits seeing each kit can only do one carb)
changing the metering rods and springs are easy if the vac signal is low use a lighter spring, if this does not help the idle quality (running rich) you will need to change out the metering rod and jet to lean the carbs at idle. it will take a bit of tuning but it's worth it in the long run.